Polyarylates are aromatic polyesters derived from dihydric phenols and aromatic dicarboxylic acids. The material based on 2,2-bis(4-hydroxyphenyl)propane (bisphenol-A) and a 50:50 mixture of terephthalic and isophthalic acid moieties (1) is offered commercially by Amoco Performance Products, Inc. under the tradename of ARDEL D-100. ##STR1## Polyarylates are high temperature, high performance thermoplastic polymers with a good combination of thermal and mechanical properties. They display excellent UV resistance and have good processability which allows them to be molded into a variety of articles.
A drawback of polyarylates is their lack of good solvent, chemical and environmental stress-crack resistance.
Polyamides comprising aliphatic diamine moieties and aromatic dicarboxylic acid moities can be either crystalline or amorphous depending on the particular moieties and concentration thereof. The crystalline versions display high melting points and provide a class of polymers with good high temperature properties. The amorphous materials have high glass transition temperatures. Both have good mechanical properties, solvent, chemical and stress-crack resistance. However, the weatherability and UV resistance and thermal performance or heat resistance of polyamides can be improved. Polyamides have been described--see, for example, J. Zimmerman, Encyclopedia of Polymer Science and Engineering, 2nd Edition, Vol. II, pp. 315-381, John Wiley and Sons, Inc., New York, N.Y., 1988. The present invention provides fully compatible and miscible one-phase polymer solutions with improved solvent, chemical, and environmental stress-crack resistance having good strength at a weld line and better weatherability and thermal performance. If the blend is not miscible, it tends to be opaque.
The advantage of having a miscible blend, over a nonmiscible blend, is that the properties of the blend are not controlled by the largest component thereof. Contrary to the present invention, in nonmiscible blends, a 1:1 ratio usually does not provide superior properties In nonmiscible blends high amounts of one or the other component are more advantageous.
The present polyarylate/polyamide miscible blends are not disclosed in the prior art.
Commonly assigned Ser. No. 208,398, which is a continuation of Ser. No. 904,907, is directed to melt processable polyamide and polyarylate polymers and copolymers made from a diamine or a diol and a diacyl compound containing 20 to 80 mole % of 5-t-butylisophthaloyl moiety. The examples are directed toward the tertiary butyl reaction with the polyamide moiety; however, there is broad mention of its attachment on the polyarylate moiety, and also possible blends with an aliphatic polyamide such as nylon 6 or nylon 66. There is no recognition of the development of a miscible blend, or the critical ratios of aromatic to aliphatic carbon atoms in the polyamide necessary to produce a miscible blend. This critical ratio is discussed fully below.
European Patent Application No. 235,384, published Sep. 9, 1987, is directed to blends of thermoplastic resins having one resin selected from a group of polycarbonate, poly(ester-carbonate) and polyarylate; in conjunction with an amorphous polyamide resin. The application shows several examples of blends containing polycarbonates and poly(ester-carbonates). Polyarylate-polyamide blends are not disclosed. This patent is directed to mechanically compatible blends but not miscible blends
U.S. Pat. No. 4,749,754 is directed to tertiary blends incorporating an aromatic polycarbonate resin, an amorphous polyamide resin and an impact modifying portion of a polyamide polyether block copolymer.
U.S. Pat. No. 4,052,481 is directed to tertiary blends incorporating a polyarylate, an aliphatic polyamide and a polyalkylene phenylene ester or a polyalkylene phenylene ester ether. The materials reportedly display good chemical resistance, thermal stability and mechanical properties. Flame retardant versions contain, in addition to the above components, aromatic halogen compounds and are described in U.S. Pat. No. 4,171,330. These blends are not miscible one-phase, however. In fact, miscibility is not disclosed in any of the references listed.
U.S. Pat. No. 4,258,154 is directed to a resin composition of an aromatic polyester-polycarboxylic anhydride and a polyamide. The reference implies that a reaction of the terminal amino group of the polyamide with the anhydride group of the polyester takes place upon blending; a chemical bond between the two polymers is created. Due to the presence of the block polymer a blend with improved mechanical properties is purportedly obtained. The observed improvement suggests that one is dealing with a two-phase immiscible system.
Polymer miscibility (particularly with complex structures such as in the polymers of this invention) is virtually impossible to predict. A very small variation in structure may lead to totally different miscibility behavior. Hence, the miscibility properties of the instant composition are unexpected and unique. A brief discussion of polymer miscibility, which will illustrate the above, follows.
In the field of miscibility or compatibility of polymer blends, the art has found predictability to be unattainable, even though considerable work on the matter has been done. In fact, "[i]t is well known that, regarding the mixing of thermoplastic polymers, incompatibility is the rule and miscibility and even partial miscibility is the exception. Since most thermoplastic polymers are immiscible with other thermoplastic polymers, the discovery of a homogeneous mixture of partially miscible mixture of two or more thermoplastic polymers is, indeed, inherently unpredictable with any degree of certainty." P. J. Flory, Principles of Polymer Chemistry, Cornell University Press, 1953, Chapter 13, p. 555. Younes, U.S. Pat. No. 4,371,672, Wang and Cooper, Journal of Polymer Science, Polymer Physics Edition, Vol. 21, p. 11 (1983).
"The vast majority of polymer pairs form two-phase blends after mixing as can be surmised from the small entropy of mixing for very large molecules. These blends are generally characterized by opacity, distinct thermal transitions, and poor mechanical properties. However, special precautions in the preparation of two-phase blends can yield composites with superior mechanical properties. These materials play a major role in the polymer industry, in several instances commanding a larger market than either of the pure components." Olabisi, Robeson, and Shaw, Polymer-Polymer Miscibility, 1979, published by Academic Press, New York, N.Y., p. 7.
A number of systems have been found that exhibit upper and lower critical solution temperatures, i.e., complete miscibility only in limited temperature ranges. Modern thermodynamic theories have had limited success to date in predicting miscibility behavior in detail. Kambour, Bendler, Bopp, Macromolecules, 1983, 16, 753.
Thus, it is seen that miscible polymer blends are not common. The criteria for determining whether or not two polymers are miscible are now well established. According to Olabisi et al., Polymer-Polymer Miscibility, 1979, published by Academic Press, New York, N.Y., p. 120:
"The most commonly used method for establishing miscibility in polymer-polymer blends or partial phase mixing in such blends is through determination of the glass transition (or transitions) in the blend versus those of the unblended constituents. A miscible polymer blend will exhibit a single glass transition between the Tg's of the components with a sharpness of the transition similar to that of the components. In cases of borderline miscibility, broadening of the transition will occur. With cases of limited miscibility, two separate transitions between those of the constituents may result, depicting a component 1-rich phase and a component 2-rich phase. In cases where strong specific interactions occur, the Tg may go through a maximum as a function of concentration. The basic limitation of the utility of glass transition determination in ascertaining polymer-polymer miscibility exists with blends composed of components which have equal or similar (20.degree. C. difference) Tg's, whereby resolution by the techniques to be discussed of two Tg's is not possible."
For purposes of this invention, a miscible blend composition has a unitary glass transition temperature. The advantage of these miscible polymer blends over a polyarylate or a polyamide polymer or over nonmiscible blends is, again, that they can be tailored to the specific mechanical properties desired without being limited to certain ratios of blend components. For example, the blends of the present invention show superior solvent, chemical, and environmental stress-crack resistance over the polyarylate polymer and superior weatherability, UV resistance and thermal performance over the polyamide polymer.